The present invention relates to an intracranial pressure relief valve and, more particularly, to a three stage valve which provides either constant pressure or constant flow characteristics in accordance with a fluid pressure differential applied across the valve.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles of the brain. The excessive collection of CSF in the ventricular spaces results in an increase in both epidural and intradural pressures. This in turn causes a number of adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Treatment of a hydrocephalic condition frequently involves relieving the abnormally high intracranial pressure. Accordingly, a variety of CSF pressure regulator valves and methods of controlling CSF pressure have been developed which include various forms of check valves, servo valves or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to some suitable drainage area of the body such as the venous system or the peritoneal cavity. Check valves operate by opening when the difference between CSF pressure and pressure in the discharge line exceeds a predetermined value.
One drawback to the use of a simple check valves in the treatment of hydrocephalus is that such a valve might open in response to normal variations in differential pressure between CSF ventricular pressure and pressure in the discharge line, resulting in hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, the differential pressure will normally increase by reason of the resulting increased ventricle height of the fluid column existing between the head and the selected drainage location. Though such an increase in differential pressure is quite normal, a check valve might respond by opening, thereby allowing undesired hyperdrainage of the ventricular spaces, which, in turn, may result in a potentially serious brain hematoma. Accordingly, it is desirable to provide a hydrocephalus pressure relief valve which is effective in shunting CSF in response to abnormal intracranial pressures while avoiding hyperdrainage in the event of normal variations in body fluid pressures.
The present invention is directed to a pressure relief valve which prevents the excessive flow of CSF in the event of sudden increases in differential pressure. In such a valve, the differential pressure between CSF and fluid in the drainage location acts to displace a movable area of a diaphragm. Such movement of the diaphragm actuates a valve regulating the passage of CSF to the drainage area. When the pressure differential is relatively small, the valve allows the passage of fluid at a flow rate sufficient to maintain a desired ventricular CSF pressure. However, a sudden increase in differential pressure, as would occur when the patient stands, causes the valve to operate essentially as a constant flow device in which passage of fluid is maintained at a relatively constant desired flow rate. A very high differential pressure, as might occur as a result of undesired clogging of the valve, causes the valve to once again operate in a constant pressure mode this time at a higher pressure, thereby preventing CSF pressure from building above a predetermined maximum safe value.
In view of the foregoing, it is a general object of the present invention to provide a new and improved pressure regulator valve for relieving intracranial pressure caused by the presence of excess CSF in the ventricles of the brain.
It is a more specific object of the present invention to provide a pressure regulator valve which avoids undesired hyperdrainage of the ventricular spaces as a result of normal increases in differential pressure.